Recently, PDP (Plasma Display Panel) applicable to a thin and large area screen has been noticed. PDP generates near-infrared ray of a wavelength of 800 nm to 1000 nm on plasma discharge, and it has been a problem that this near-infrared ray induces improper operation of a remote controller of home electric appliances. In addition, because an optical semiconductor element used in a CCD camera, and the like has a high sensitivity in near-infrared region, the removal of near-infrared ray is required. Under such circumstance, near-infrared ray absorption material having high near-infrared ray absorption ability and high transparency in visible region has been required.
As near-infrared ray absorption material, material added with a dye capable of absorbing near-infrared ray has widely been known. As such a near-infrared ray absorbing dye, a cyanine based dye, polymethine based dye, squarylium based dye, porphyrin based dye, a dithiol metal complex based dye, phthalocyanine based dye, a diimmonium based dye, and the like have conventionally been used. Among these, a diimmonium based dye has been widely used due to its high near-infrared ray absorption ability at a wavelength of not shorter than 900 nm and high transparency in visible light region (for example, see U.S. Pat. No. 6,255,031 and U.S. Pat. No. 6,522,463). As near-infrared ray absorption material for an optical semiconductor element, one containing a copper phosphate-based compound has been also used (for example, see U.S. Pat. No. 5,567,778).
Furthermore, because PDP generates discharge in gas atmosphere mainly composed of rare gas, in particular neon, encapsulated inside a panel, and by means of vacuum ultraviolet ray generated on the discharge, fluorescent substances, R, G and B installed in a cell inside the panel are made to emit luminescence. In this emission process, electromagnetic wave unnecessary to PDP operation is also discharged simultaneously, and therefore, shielding of electromagnetic wave is also required. In addition, to suppress reflection light, an antireflection film and a glare prevention film (an antiglare film) are also necessary. Therefore, an optical filter for a plasma display is generally prepared by laminating a near-infrared ray absorption film, an electromagnetic interference shielding film and an antireflection film on glass or an impact absorption sheet as a supporting substrate. Such an optical filter for a plasma display may be used by mounting at the front surface side of PDP or by directly adhering using an adhesive or a pressure-sensitive adhesive.